Midfielder James was booked for the fifth time this season against Crawley on Saturday and sits out one match while striker Mooney completes a three-game ban.
Defender Elliot Omozusi missed the leaders' surprise 3-2 home defeat through suspension and is set to return at right-back.
Winger Dean Cox was also absent against the Red Devils due to illness so he will be assessed ahead of kick-off.
Myles Weston is a doubt for Gillingham's Boxing Day clash at home to League One leaders Leyton Orient but Adebayo Akinfenwa should be okay.
Winger Weston was forced off after just 22 minutes of Friday night's 2-1 win at Tranmere nursing a hamstring injury and will be assessed.
Akinfenwa was making his first league start since September and, having bagged a matchwinning brace to see off Rovers, was substituted with nothing more than cramp.
He came in for striker Danny Kedwell, who is again set to miss out with a possible hernia, while midfielders Chris Whelpdale (leg) and Danny Hollands (knee) continue to be monitored.